I bought the item below on Amazon for £7.99 to remove all the light leaks from the back of my 8" Newtonian. It works a treat. It's an extra large black triple layer shower cap 
I've just ordered another for the other end and reckon that means I can take darks at almost any time of the day
[Update] FWIW: Took a set of darks tonight and they look like the best I have ever taken. I'm really surprised by how much light leakage there was at the back there.
Here's what one of my ASI1600MM Pro 300 sec darks looks like now. It's not zero amp glow, but it is pretty close :
I've just ordered another for the other end and reckon that means I can take darks at almost any time of the day [Update] FWIW: Took a set of darks tonight and they look like the best I have ever taken. I'm really surprised by how much light leakage there was at the back there.
Here's what one of my ASI1600MM Pro 300 sec darks looks like now. It's not zero amp glow, but it is pretty close
: